Drop channel pulse multiplex system



April 3, 1951 D. D. GRIEG 2,547,001

DROP CHANNEL PULSE MULTIPLEX SYSTEM Filed Jan. 26; 1944 7 Sheets-Sheet 1 April 3, 1951l D, D. GRIEG 2,547,001

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Patented Apr. 3, 1951 DRG?? CHANNEL PULSE MULTIPLEX SYSTEM Donald D. Grieg, `Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application January 26, 1944, Serial No. 519,757

l2 Claims. l

This invention relates to communication systems and more particularly to communication systems provided with means for dropping or replacing one or more channels at a branch station intermediate the principal terminals of the system.

Systems for multiplex communication by means of interleaved, timed, trains of impulses have heretofore been proposed. In these systems, generally the segregation of the channels is accomplished by timing selector means rather than by using lters, as in the case of multiple carrier multiplex systems. In such pulse multiplex systems, it has been proposed. to provide branch circuits for selecting one or more of the channels at diierent branch points. However, in these proposed systems, the pulses dening channels selected at the branch circuit continue through the line to thel principal receiving terminal. As a consequence, it has not been readily possible with these proposed systems to communicate between the branch terminal and both of the principal terminals without waste channel space.

It is an object of the present invention to provide a multiplex pulse transmission system in which one or more channels carried by a common transmission medium may be selected at an intermediate terminal and the selected channel or channels may be suppressed in the common transmission medium so that the pulses do not continue to the ultimate terminal and, where desired, to replace the suppressed pulses with other signal modulated pulses at the branch terminal.

It is a further object of my invention to provide, at a branch terminal in a multiplex pulse transmission system in which the several channels are defined by a resultant pulse train in a common medium, a transmitter arrangement for supplying pulses defining a communication chann nel timed with respect to the pulses in the multiplex system so that they will nt into gaps or spaces in the resultant train in the common me dium of transmission.

It is a still further object of my invention to provide a branch terminal in a multiplex pulse communication system in which channels to be selected at the branch terminal may be controlled by synchronizing energy applied to the pulses at the transmitting end.

It is a still further object of my invention to provide a multiplex pulse communication system wherein communication may be had between the principal terminals of the system, between a principal terminal of the system and one or more branch terminals and between one ofthe branch terminals and another of the branch terminals;

According to a feature of my invention, aplii-' rality of trains of pulses having a given cadence frequency are applied to a common medium'ata rst terminal for connection over the common medium to a second terminal. Coupled to the common medium, intermediate the .rst and'second terminals, are provided one or more branch terminals. The branch terminals may be provided with means for selecting one or more of the channels, means for vsuppressing the selected channels in the common medium and means for inserting a new series' of pulses timed to occupy the spaces left by suppression of the pulses in the common medium. The branch terminals may be arranged lso that successive branch terminals will select differently timed channels or channels of the same timing so that communication may be had among the various terminals, as desired;

According to a further feature of my invention, the pulses of each channel may be supplied with signal modulations modulating the pulses, either in time position, amplitude, Width or the like. In addition, at one of the teminals, means may be provided for applying a synchronizing modulation to the pulses of a channel to be selected and selective means may be provided in the branch terminal responsive to the synchronizing signal for selecting from the common medium the desired channels.

A better understanding of my invention and the objects and features thereof may be had from the particular description of an embodiment and certain modifications thereof, made by reference to the accompanying drawing, in which:

Fig. 1 is a simplified block diagram of 'a communication system incorporating the features of my invention;

Fig. 2 is a set of curves illustrating the operation at various branch terminals vin accordance with my invention; V

Figs. 3 to 6 inclusive, taken together and` are ranged in accordance with the showing of Fig. '7, illustrate in block diagram a circuit arrangement in accordance with my invention, Fig. 3 showing a principal or west terminal station, Fig. i a branch terminal A, Fig. 5 branch terminals B and C and Fig. 5 the other principal or east terminal of the system; A v

Fig. 8 is a wiring diagram oi'va time modula-l tor which may be used as a part of thecircuit.

in accordance with my invention;

C. At branch terminal A is provided a west-east translator circuit IBA and a pulse suppressor and coupler circuit IEA together with an east-west translator MA and a suppressor and coupling unit |F. Similar west-east translators and suppressor and coupler circuits 13B, IB, IB, |5E and ISC, IGC, ISC and |5D are shown, respectively, at branch terminals B and C.

*It-is'understood that terminal I0 is a multiplexv transmitter arrangement which may supply a large number of channels. For simplicity o1' explanation, however, the circuit arrangement, as illustrated in more detail in Figs. 3 to 6,-inclusive,'shows only nine channels numbered I to 9, inclusive..

Referring-to Fig. 2, curve a illustrates the channels which may be transmitted from terminal lli. It will-be noted that in this curve channel 8 lhas beenfomitted. This channel may be supplied at a subsequent branch terminal as will be explained below. At branch terminal A selection of channels I, 4 and 9 is made, see curve b. Channel I, however, is used only as a synchro.- nizingvchannel and is not suppressed at this terminal. However, channels ll and 9 are suppressed, as shown'at curve c. Other channels A and SA, as well as a channel to fill in the blank of 8, numbered 8A, are supplied at this branch terminal so that the output will be substantially in accordance with the illustration of curve d. At branch terminal B channels 2 and 5V are selected. Ighese selected channels are also suppressed at this branch terminal and new channels 2B and 5B are substituted in their stead, as can be seen fromA curves e, f and g. At branch terminal C, channels I, 3 and 9A are selected. At this branch terminal a further channel 9C is reinserted but the space for channel 3 is left blank. This can be seen in curves h, i and j. As a consequence, the east terminal I2 receives the remaining channels l, 6 and 'I which come directly from terminal I0, channels 4A and A directly from branch terminal A, channels 2B Y and 5B directly from branch terminal B and channel' 9C from branch terminal C. At the same time, intercommunication between branch A and branch C is carried on by means of channel 9A.

The above explanation briefly traced only the communication in the west-east dircetion. It is, of course, udnerstood thata-similar transmission between terminals I2 and I0 and the various branch terminals may be carried on in the eastwest direction.

' YTurning now to Figs. 3 to 6, inclusive, a more complete description of the operation of the system may be had. In Fig. 3 is shown a rst terminal I0 which may comprise incoming signal lines |0I to |29, inclusive, coupled through hybrid coils III to' IIS, inclusive, to modulators I2! to |29, inclusive. 'I'hese modulators may be of any desired type but are preferably of the type producingvtime displacement modulation of pulses.

GCI

In order to eiect this time modulation, energy from a base wave source |30 is applied over individual phase Shifters itl to |39, inclusive, to the respective modulator circuits I2I to i253. The phase Shifters are adjusted so that the individual trains of pulses for the separate channels will be displaced in time to provide a single resultant train in the common output. In addition, the lines I itl from. dernodulator circuits, not shown, are coupled to hybrid coils i I I to IIS and to lines lili to |59 for communication in the opposite direction. This will serve for normal two way communication over lines loim9, the hybrid coils preventing energy received from the demodulators from feeding into the modulator circuits.

Channel I may be used as a synchronizing channel and to this end a synchronizing source I5I supplying energy at frequency jl is coupled to modulator |2I. In the output of the other modulators |22 to |29 are provided switches M2 to |49, inclusive, so that il any of these channels is not being used for communication tle switches may be opened so that pulses corresponding to this channel will not be applied to the line. As illustrated, switch |618 is opened so that no pulses corresponding to channel 8 are applied to the transmission line iii. In addition, two other synchronizing sources |52 and |53 supplying energy at f2 and f3 are provided. Source 52 is provided with an adjustable switch I5@ and source |53 with an adjustable switch |55 for selectively applying these synchronizing signals to modulators |22, |23, 25, |21 or |22, as desired. It should be clear that other contacts may be provided so the synchronizing signals may be applied to any of the channels, if desired. In the position shown, energy from |52 is supplied to modulator |22 and energy from |53 is supplied to modulator |25 providing a special synchronizing or selector modulation to each oi channels 2 and 5. Phase Shifters I3! to |39, inclusive, are so adjusted that the pulse outputs from |2I to |29, inclusive, will be applied to the transmission. line |52 in timed spaced relationship providing a resultant train of waves corresponding to curve a of Fig. 2,

In Fig. 4 is shown the west-east selector system for branch terminal A. The pulses incoming over line |55 are applied to the cle-blockerselector 2e! and from this selector to demodulator 2li. The output from demodulator 2|! is supplied over filter 22| to de-blocking oscillator 23| which serves to produce timed pulses, preferably of substantially rectangular form, for application to the dee-blocker selector circuit.

Preferably, the de-blocker oscillator 23| is normally timed to provide a pulse spacing slightly greater than the interval spacing of the pulses of any one channel. As a consequence, when the pulses arrive at cle-blocker 20| they are selected in rotation until such time as channel I is received. Upon receipt of channel I, however, demodulator 2H produces an output tone corresponding to frequency fl applied from source I5! to the modulator |2I. rThis tone frequency 7' I is selected by iilter 22| and serves to synchronize cie-blocking oscillator 23H with the Vinterval timing of the pulse channels. As a consequence, the progression of selections is halted and the selected channels are continuously received thereafter. An understanding of the details ci this particular selector arrangement ris not necessary to a complete understanding of my invention and is therefore not set forth in detail herein although further' explanation is given later in connection 'with Fig. l0. For a more complete understanding of this feature, reference may be had to copending application, entitled Multiplex Synchronizing System, Serial No. 514,998, illed December 20, 1943, now Patent No. 2,418,11, granted April 1, 1947.

At station A in energy 'from cle-blocking oscillator also applied over delay networks 236 and 2te to other cle-blocker selectors 2id and EIS. Also, the pulses from line l5@ are applied to these (ie-blocker selectors so that correspond;- ing channels may he selected. In the present description, for purposes of illustration, it is assuined that delay networks Zilli and 2tlg are adjusted to select channels l5 and 9, respectively. These selected channels are then dernodulated in deniodulators 225 and 2,139 and applied to suitalole reproducers, not shown. The selectors 21H, 2id and 25S serve to select pulses i, 4 and 9 by selector pulses lil, ht and b5, shown compositely in curve b, Fig. 2. The selectors also serve to clip the composite pulses at clipping level 90 so that only pulses l, d and 9 remain.

The cle-blocking oscillations from delay networks 2M, 2tlg are further conducted to phase rever-sers and 2539, respectively, providing suitable reversed wave forms cil and e9 with the same timing as the selector pulses bfi and These sets of pulses may he combined in a coupler mixer Edil applied to channel suppresor 2lli. In sup-Dresser 2M the phase reverse ce-blocling oscillator pulsesl and the channel pulses are combined, as shown at curve c of Fig. 2, suppressing channels l and 9 from the common medium. These suppressid channels leave gaps in the pulses; applied to the common rnediuin, as shown by the pulses of clipping level 9! of the suppressor.

Energy from de-lc-locking oscillator 235 may he further applied to a hase wave source 2% operating at substantially the saine frequency as hase wave source itil of Fig. 3. The rie-blocking oscillator' pulses serve to synchronize base wave source with the incoming pulses or may serve directly to generate waves of this base frequency synchronized with the incoming selected pulses. Energy from the base wave source 2&3 is applied over phase Shifters 2M, Edd and 265 to modulaters and serving to produce channels 43A, 8A and @A corresponding to channels t, il and Si. Phase shifters 2M, 2da and Zll are adjusted so that the produced pulses of channels @1 SA ar @A will properly sandwich in to the co 1g gaps in the common medium. These rulses are then applied to line ld through 4 g circuits 5252 and 269, producing in the a resultant train of pulses, as shown at rig. 2. Coupling circuits 2te, 268 and 2&9 may not ce necessary. However, it is preferable to have these circuits to prevent pulses from lines il feeding down to the separate modulators. In the absence of proper' matching they might reilect from the modulators causing interference in the transmission line. Switches 2M, 218 and Q'le are provided to disconnect modulators 25d, 253 and 25B from line ll? in case communication on these channels is not desired at this point.

` Similarly, switches 28a and 2c@ may be provided :all

tion l2` selection of the channels to be dropped is made through the medium of the signals f2 and f' rcni sources ldZ and l5@ of Fig. 3. In the position indicated, channels 2 and 5 are selected. These pulses are applied over de-hlocker-selector circuits 302, @at to deniodulators SI2, Sife, respectively. The synchronizing signals from dernodulators 322 and 325 are applied over filters 322 and to de-bloclzing oscillators 332, S35, respectively, to cause automatic selection of these channels in the saine manner that channel was selected at branch station A. The output from demodulators H2 and SI5 are applied over lters S82 and 3535 to suitable reproducers. The filters :i232 and 3&5 serve to remove from the signalling energy the synchronizing frequency f2 and f3 so that they will not he present in the reproducers. The selection of these channels at station B is shown at curve e, Fig. 2, in which the pulses are clipped at clipping level 32. o

The pulses from the de-blocking oscillators $52 and 335 are applied over phase reversers 342 and Sile to coupler Se@ which serves to combine the reversed pulses and these reversed pulses are applied to channel suppressor @di together with the incoming pulses from line ld producing a resultant curve corresponding to f, Fig. 2, clipped at clipping level The output from de--blocking oscillator 332 is applied to a base wave sourc fili@ which furnishes a modulating base wave over phase shitters 355 to signal modulators 362, respectively. These modulators produce other channels 5l?, corresponding to the 'supchannels 2 and 5 which channels are applied over couplers 3:2, 315 to line i 5@ producing resultant wave train in line itil, shown at g, Fig. 2.

This resultant train is applied at branch station C to dev-blocker selectors 491, dit and H9 serving to select channels l, 3 and 9A, respective- As in the case of branch n, channel l serves for synchronizing in this case. Accordthe signals for de-hlocirer its re applied to dernodulator il i and a filter itl in the output of this demodulatcr serves to select the synchroniZ-lng frequency fl from the signal synchronizing cle-blocking oscillator 3l with the incoming pulses. Energy from cle-clocking oscillator si is applied to cle-blocking selectors il! 3 and i9 over delay networks 1&3 and lil adjusted properly to select the channels. The outputs from selectors @i3 and lill! are applied to demodulators 42E and @29, respectively, and from there to suitable reproduoers, not shown. This selectiny operation serves to select channels l, dA, as shown at curve h, Fig. 2, clipped at he clippirrT level 9d.

The cle-blocking oscillations from the output of delay networks its and (its are reversed in phase reversers lli-l2 and @Se and combined in coupler for application to channel suppressor 332 producing the resultant wave, shown at curve -Fig. 2, clipped at level 95. From the output of delay network 60S is supplied 'a synchronizing connection base wave source Mil, which, over phase shifter. elle, serves to produce the desired modulating wave for modulator 459 producing in the output a channel SEC. rIhis channel @C coupled. to line E over coupler rifle producing in line le) the resultant pulse train shown at curve i of Fig. 2. it should loe noted that in this curve channel 3 was not reinserted so that a gap corresponding to this channel appears in the-resultant pulse train.

The pulses from line itil continue to east termnal I2, shown in Fig. 6. In this terminal the pulses from the line may be applied to the several (ie-blocking selectors 5I l to 519, respectively, over switches 55| to 559. As shown, there is no incoming signal corresponding to channel 3 so switch 553 remains open and the channel selector 5l3 is therefore ineffective. The incoming pulses from channel i are applied over cle-blocking selector 5H to demodulator 52l, the synchronizing frequency fl is selected at filter 552i and applied to de-blocking oscillator 55E to synchronize this oscillator with the incoming signals, as explained above. Since channel l preferably serves as a monitoring channel the output from demodulator 52! is supplied also over lterg53l, which serves to block out synchronizing frequency fl, and over a hybrid coil 55l and a line 5l! to the monitoring receiver 5i! l.

Pulses from de-bloclring oscillator 55l are also applied over delay networks 552 to 559, respectively, to de-blccker selectors 512 to 5l9 in the outputs of which are coupled demodulators 522 to 529 which serve to demodulate the signals incoming over the several channels. The demodulators are coupled over hybrid coils 552 to 555, respectively, and lines 5'l2 to 579, respectively, to their respective signal reproducers. The other terminals of the hybrid coils 55! to 559, inclusive, may be coupled over the separate lines 58B to modulators which, in conjunction with the reproducers connected to lines 572 to 5w, will afford two way audio communication.

It will be readily appreciated that the system disclosed herein is merely illustrative of a multiplex system incorporating the principles of my invention and that other branch terminals may be provided, as desired. Furthermore, any known type of transmission and selection circuit may be used in place of the specific types illustrated without departing from the scope of my invention.

In order more clearly to disclose the structural examples of a transmitter in accordance with my invention, reference may be had to the circuit diagram of 8. In this ligure, energy from a signal source indicated in Fig. 3 as connected to line il is applied over a lter 2G to modulating circuit l2l, the output of which is coupled t the outgoing line I5. Incoming.,r signal frequencies are applied over filter 2B, which is tune to exclude the synchronizing frequencies, to a tube 3l). Simultaneously, synchronizing modulations from source l5! are applied to another tube 3l. The outputs of these tubes are combined in line 32 producing a resultant mixing of the signals and synchronizing frequencies. This resultant mixed wave is applied over separate transformer windings 35 and 35 to a mixing transformer arrangement 33. Simultaneously, energy from a base wave source 38 is applied to mixing transformer 33 by means of coil 35. Secondary coils 3l and 38 are also coupled to 33 to extract from there the mixed signals. Coils 31 and 53 are coupled to a pair of triode rectiers 39 and 55 symmetrically biased. The base wave source |323 preferably has a frequency corresponding to the desired cadence frequency T of the pulses to be produced.

Since tubes 3S and 5.5 constitute a full wave rectifier, an output wave of the form shown at 25A will be produced in the absence of any input signals from sources H3! or l5l. This wave is applied to a pulse Shaper @I producing a plurality of symmetrically spaced pulses having cadence frequency of T. Upon application of energy from sources ll and l5l the symmetry of the rectifier circuit 39, it is upset producing pulses having substantially the same cadence frequency as before but at an unsymmetrical repetition rate, as shown in curve 25B. Thus, as the signals are applied to modulate the base wave energy a time displacement of the pulses in the output oi' pulse shaper il is provided. While Fig. 8 discloses a transmitter circuit Such as shown at l2! of Fig. 3, it is clear that the same type of transmitter may be used in all of the different circuits. However, in systems in which no synchronizing signals are to be applied, source I5I may be omitted. Furthermore, a phase shifter, for the base wave source energy applied to the separate modulators, is preferably provided in order to secure the desired time spacing of the pulses to produce the resultant sandwiching or interleaving of the pulse channels on line |50.

In Fig. 9 is illustrated the coupler and mixer circuits corresponding to 25,3 and 2M of Fig. 4. The mixer circuit 2:35 comprises a tube 5I into which the inverted de-blocking oscillations phase displaced with respect to one another, as shown at EiA, 52A, are fed. These pulses are fed to separate grids in tube 5l so that each of them independently produces an output impulse in line 53S providing a resultant curve such as shown at 53A. The suppressor circuit 2M comprises a pair of mixing tubes 55, 55. Into tube 50 is fed the incoming pulse train from line 55, as shown at 53A, while the wave 53A is fed into tube 53. The two plate circuits of tube 5G, 53 are connected in parallel producing a resultant output wave shown at 55A. This resultant Wave is fed over coupling condenser 55 to clipper tube 5l. A sufficient bias is applied to the grid of tube 5l over resistor 53 so that only the peak boosted pulses are repeated, applying to line 55 at the output of tube 5l a series of pulses. At the input of tube 55 is provided the usual grid resistance 5&3 shunted by a rectiiier 55. This rectiner 55 is usually known as a D. C. restorer and serves to assure iat the amplitude of pulses from 53A are at all times o the same value. By having this value iixed, the clipping action of tube 51 may be properly adjusted to only clip so much of wave 54A as is necessary to produce the desired resultantoutput pulses.

It is clear that other couplers in line |50, such as shown at Sl5, etc., may be of similar form to the coupler 255. These couplers serve merely to prevent the pulses transmitted over line i5 from being fed back to the modulators 362, 265, just as above explained When discussing couplers 266 to 259. In place of this type of vacuum tube coupler, suitable bridge or hybrid coil arrangements may be used in some instances.

A typical demodulator circuit is shown in Fig. l0. This circuit corresponds to the selector demodulator arrangement 352, Sil of Fig. 5. It should be distinctly understood, however, that the same type of circuit may be used for demodulation in the other parts of the system. According to this arrangement, the train of pulses from line |50 is fed over line 6E! to mixer tube El. At the same time, de-blocking pulses from de-blocker oscillator 332 are fed to another separate grid oi tube 5I. These de-blocking pulses serve, in conjunction With the incoming pulses timed to add thereto, to produce an output series of pulses in tube 6l Thus, for example, as shown in curve e of Fig. 2, the cle-blocking oscillator may serve to produce a plurality of rectangular pulses timed in spaced relation with the pulses 2 and 5. Tube 6| is also biased to serve as a clipper so that only the boosted pulses 2, 5 appear in the output thereci. A. I). C. restorer rectifier tube 52 maybe provided across the input from de-blocking oscillator 332 to assure that the incoming cle-blocking pulses lare of a proper level to Work with the clipper circuit of 6l to leave only the desired output pulses.

The output pulses from 5| are spaced with the same repetition frequency and have the same cadence frequency as the original modulated pulses from a modulator, such as shown in 8. The pulses are applied to one of the grids oi a de-modulator tube 63 and cause tuned circuit G5. connected to the other grid of this tube to oscillate at a desired frequency producing in the output of tube 63 a combined Wave in the form oi a combination of the Wave generated in 64 and the incoming pulses. Circuit 64 is preferably tuned to some harmonic of the cadence frequency of the input pulses so that as the repetition rateJ is varied, due to the modulation signals, the output pulses will be raised to different levels depending upon the spacing. Accordingly, in the output oi tube 53 will appear a modulation envelope of pulses carrying signal modulations thereon. A low pass iilter 65 is provided to remove from this demodulated signal envelope the pulses of higher frequencies that dei-lne the signal envelope. The output synchronizing signal is passed over filter 322 tuned to pass only the synchronizing irequency f2 which, in turn, serves to synchronize the operation of dea-blocking oscillator 332. The remaining demodulated Waves are passed over a filter 382 tuned to exclude the synchronizing signal to a suitable reproducing device. It should be distinctly understood that in cases Where the deblocking oscillator is not controlled directly by the output Waves, the cie-blocking pulses applied to tube .Si may come from a suitable delay line dependent upon the channel to be selected.

In the circuits described so far, it has been assumed that the modulated pulses are being transmitted at their normal frequency so that separate lines are required for the West-east and eastwest transmission. The signal pulses, however, may be used to modulate higher frequency carriers and a single transmission line used as a transmitting medium between the various terminal stations. Such a circuit arrangement is shown in Fig. 11. The West-east transmission takes place at carrier frequency Fi while the eastwest transmission takes place at a different frequency F2. At any branch terminal, for example, a terminal corresponding to that shown in Fig. 4, Fl, F2 may be separated by suitable input filters 'H and 3l. rIhe filtered signals may be detected at l2, 82, respectively, and applied to the deblocker demodulator circuits, such as shown below the line A-A of Fig. 4.

The combined suppressi plied to the respective ci 83, serving to bias an a ube, for example, to out so as to the pulses corresponding to the desired channels. ing pulses from S3 are on ers or couplers and from there to the transmission line. The channels to be serted after suitable modulation phase lg ere modulators le, 35, respec- ..,y, together with. carrier frequency energy of and from sources es Bil. These pulses produced in modulators $5 are then.

also applied to mixers th proper relation to fill in gaps the resultant pulse train on the common medium.

As described above, my invention has been-appliedV only to multiplex signallingg It is clear that it may be desirable to selectA and suppress pulses in a line even though multiple channels are not present. For' example, letl it be assumed that only one signal channel is to be transmitted selectively between terminals is and l?? of Fig. l., or to one of the branches A, B and C. It is clear that the signals may be selected at branch A, for example, suppressed in that station and a new signal sent on to the next branch B and so on. Byproviding suitable synchronizing sig,- nals at i8, and respective selectors for these lsignals at stations A, B, C', etc., it is clear'tha't the pulses may be characterized so as to provide connections selectively between lil and 'any one ofthe branch circuits. These branch eircuits could then. communicate furtherby" the system of suppression and remodulation, las4` out'- lined above. 'y e' "I It is clear that while thisy system is best adapted for communications carried over lines, the principles of my invention may ce applied-` to radio transmission. In this case, the carrier ire-quen'- cies such as Fi, F2 may be radiated from 'an'- tennas instead of being transmitted over the separate lines. j While I have 'described in considerable ldetail specific embodiments of my invention, this description is to be considered merely vas illustrative of the invention and notas a limitation on the scope thereof, as set 4forth in the objects of my invention and the accompanying claims. What lis claimed is: l. In a communication system comprising a first terminal for transmitting a plurality of pulser trains, the pulses of each train being timed with respect to those of the other trains tov provide a resultant train of pulses, a second terminal for re,- ceiving the pulse trains from said iirstterminal and a common medium interconnecting saidterminals, a plurality of branch terminals, cach coupled with said medium and comprising means for selecting the pulses corresponding to a diierent one of said trains, means at each branch for suppressing the selected pulses leaving correspond-v ing gaps lin said resultant train, means at the branch 'terminals for producing other pulses, means for timing said produced other pulses 'to correspond in time with said selected pulsesand meansv for applying said produced timed pulses to said common medium Where 'the cranclies are lcoupled thereto and in said gaps .left by suppression cf said selected pulses.

' 2. A communication system including a singie pulse-transmitting circuit, a plurality ci 'stations effectively connected at points on said circuit, means for applying to said circuit regularly-recurring synchronizing pulses, each of said stations having assigned thereto a predetermined period in the intervals between said pulses, said period having a predetermined time relation to said pulses, and said relation being dii'erent for each of said stations, and means at each si tion for applying to said circuit modulated signal pulses and lor selecting a period for the occurrence of said signal pulses corresponding tothe period assigned to the station to which said signal pulses are to be transmitted, each station being adapted to detect said signal pulses during the period assigned thereto only.

3. A communication system including a plurality of stations, a single pulse-transmitting circuit connecting said stations, means for applying' regularly-recurring synchronizing pulses to said circuit, each of said stations being adapted to detect modulated signal pulses applied tosaid circuit and occurring during a predetermined period only, said period having a predetermined 'time relation to said synchronizing pulses and said relation being different for each of said stations, and means at each station for applying to said circuit modulated signal pulses capable of being detected by another of said stations as aforesaid, and for selecting the period during which said signal pulses occur.

4. A communication system including a plurality of stations, cables connected to each of said stations and connecting said station to the preceding and succeeding stations respectively, means for applying regularly recurring synchronizing pulses to the circuit constituted by said stations 'and said cables, each of said stations being adapted to detect modulated signal pulses applied to said circuit and occurring during a predetermined period only, said period having a predetermined time relation to said synchronizing pulses and said relation being diiierent for each of said stations, and means at each station for applying to said circuit modulated signal pulses capable of being detected by another of said stations as aforesaid, and for selecting the period during which said signal pulses occur.

5. A communication system including a single pulse-transmitting circuit, a plurality of stations eiectively connected at points on said circuit, means for applying to said circuit regularlyrecurring synchronizing pulses, each of said stations having assigned thereto a predetermined period in the intervals between said pulses, said period having a predetermined time relation to said pulses, and said relation being different for each station of the system,`means at each station for generating signal pulses, for selecting periods for the occurrence of said pulses `corresponding to the periods assigned to the other stations of the system, for modulating said signal pulses and for applying said signal pulses to said circuit, each of said stations including at least two channels, means at each station for diverting synchronizing pulses applied thereto to one of said channels and signal pulses applied thereto to another of said channels, vand means in the second of said channels for detecting signal pulses diverted thereto and occurring during the period assigned to the station in which said detecting means are located.

6. A multiplex communication system of the type in which messages are transmitted in separate channels by pulses of separate trains of pulses, each train of a given cadence frequency, in accordance with signal modulations, comprising a rst terminal for transmitting said pulse trains, a second terminal for receiving said pulse trains, a common medium interconnecting said first and second terminals, a branch terminal intermediate said first and second terminals coupled to said common medium, means at said branch terminal for selecting and demodulating the pulses corresponding to a given channel, means at said branch terminal for preventing access of the pulses corresponding to the selected given channel to said second terminal, means at said rst terminal for giving to the pulses of Said channel to be selected a predetermined modulation characteristic, and means at said branch terminal responsive to said predetermined modulation for selecting said pulses of predetermined modulation. f

7. A multiplex communication system of the type in which messages are transmitted in separate channels by pulses of separate trains of pulses, each train of a given cadence frequency, in accordance with signal modulations, comprising a nrst terminal for transmitting said pulse trains, a second terminal for receiving said pulse trains, a common medium interconnecting said irst and second terminals, a branch terminal intermediate said first and second terminals coupled to said common medium, means at said branch terminal for selecting and demodulating the pulses corresponding to a given channel, means at said branch terminal for preventing access of the pulses corresponding to the selected given channel to said second terminal, a source of synchronizing signals at said iirst terminal, means for selectively applying said synchronizing signals to one oi said channels to produce a pre- 'determined modulation thereof, and means at said branch terminal responsive to said predetermined modulation for selecting said one of said channels.

8. A multiplex communication system of the type in which messages are transmitted in separate channels by pulses of separate trains of pulses, each train of a given cadence frequency, in accordance with signal modulations, comprising a nrst terminal for transmitting said pulse trains, a second terminal for receiving said pulse trains, a common medium interconnecting said rst and second terminal, a branch terminal intermediate said first and second terminals coupled to .said common medium, means at said branch terminal for selecting and demodulating the pulses corresponding to a given channel, means at said branch terminal for preventing access of the pulses corresponding to the selected given channel to said second terminal, a source of synchronizing signals at said nrst terminal, means for selectively applying said synchronizing signals to one of said channels to produce a predetermined modulation thereof, and means at said branch terminal responsive to said predetermined modulation for selecting vsaid one of said channels, means at said branch terminal for producing a further train of pulses, timing means for timing said produced pulses to correspond in time with said selected pulses, and means to apply said produced timed pulses to said common medium where the branch terminal is coupled thereto.

9. A communication system oi the type in which messages are transmitted by time displacement of pulses of a given cadence frequency, in accordance with signal modulations, comprising a iirst terminal for transmitting said pulses, a second tei iinal for receiving said pulses, a common medium interconnecting said first and second terminals, branch terminal intermediate nrst and second terminais coupled to said common medium, means at said branch terminal for selecting and demodulating pulses, means at rr. controllable from one of said first and second terminals for suppressing the selected pulses, means at said first terminal ier givingr to said pulses a predetermined modulation characteristic, and means at said branch t minal responsive to said predetermined modulation for selecting pulses ci predetermined modulation.

i0. A communication sy Lem comp-rising a .first terminal, means for transmitting from said first terminal plurality oi trains of pulses, means i'or timing the pulses or each said trains `with AAN,

respect to the pulses of the other trains to provide a resultant train of spaced pulses, a second terminal station for receiving said trains of pulses, a common medium interconnecting said terminals, at least one terminal intermediate said rst and second terminals coupled to said common medium, means at said branch terminal for prod cmg other trains of pulses, means at said bra :h terminal for applying said produced train of pulses to said common medium where the branch terminal is coupled thereto in such timed relation with said resultant train of pulses that said-produced pulses are interleaved in said resultant train, means at said rst terminal for applying a synchronizing modulation to one of said pulse trains, means at said branch terminal for selecting said modulated pulse trains in response t0 said synchronizing modulations, means at said oranch terminal for suppressing said selected modulated pulse train,kand means for timing said produced train of pulses to correspond in time with said selected train of pulses, whereby said suppressed train of pulses is replaced by said produced train of pulses.

11. In a communication system having a first terminal for transmitting a plurality of pulse trains, each train comprising a communication channel, the pulses of each train being timed with respect to the others to provide a resultant train of pulses, a second terminal for receiving the pulse trains, and a common transmission medium interconnecting said terminals, an intermediate branch terminal coupled With said medium for selecting one of said channels and supplying a new channel to replace the selected channel comprising selector means for selecting the pulses of a train corresponding to said one channel, suppressor means for suppressing the pulses corresponding to said selected channel at the branch terminal leaving gaps in said resultant Wave train, means at the branch terminal for producing a train of pulses corresponding with the pulses of said one channel, timing means for 14 timing the produced train of pulses to correspond with the selected pulse train, means for applying said produced timed pulses to said common medium Where the intermediate branch terminal is coupled thereto to supply a new channel replacing said selected channel, means at said rst terminal for applying a predetermined mod ulation to the pulses oi one of said trains to provide a synchronizing channel, and means at said branch terminal responsive to said synchronizing channel for causing said selector means to select the pulses defining said one channel. l2. In a communication system, a plurality of terminals, a medium for intercoupling said terminals, means for transmitting time multiplexed pulses over the medium in ,a plurality of channels, control means at one oi said tWo terminals for providing denial of access to another of said terminals of at least one preselected channel fof said plurality of channels,I said control means comprising means for modulating pulses of said preselected channel Iwith identifying signals.

DONALD D. GRIEG.

CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTSy 

